The present invention relates to modification of a crystalline aluminosilicate zeolite catalyst having a Constraint Index of from about 1 to about 12, e.g. ZSM-5, to reduce external acid sites thereon and a process for preparing high viscosity index (VI) lubes employing the modified catalyst.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalyst properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction within which there are a number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for absorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline aluminosilicates. These aluminosilicates can be described as a rigid three-dimensional framework of SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of aluminum to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given aluminosilicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. The zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite Z (U.S. Pat. No. 2,882,243); zeolite X (U.S. Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite ZK-5 (U.S. Pat. No. 3,247,195); zeolite Beta (U.S. Pat. No. 3,308,069); zeolite ZK-4 (U.S. Pat. No. 3,314,752); zeolite ZSM-5 (U.S. Pat. No. 3,702,886); zeolie ZSM-11 (U.S. Pat. No. 3,709,979); zeolite ZSM-12 (U.S. Pat. No. 3,832,449); zeolite ZSM-20 (U.S. Pat. No. 3,972,983); ZSM-35 (U.S. Pat. No. 4,016,245); ZSM-38 (U.S. Pat. No. 4,046,859); and zeolite ZSM-23 (U.S. Pat. No. 4,076,882), merely to name a few.
U.S. Pat. No. 4,461,845 teaches a method for reactivating a steam-deactivated catalyst comprising a zeolite having a silicon/aluminum atomic ratio of at least 2. The method involves contact with an aluminum compound at elevated temperature, followed by contact with an aqueous acid solution. U.S. Pat. No. 4,477,582 teaches a method for reactivating a steam-deactivated catalyst comprising a zeolite having a silicon-aluminum ratio of at least 3.5. The method of this patent involves contact with an alkali, alkaline earth or transition metal salt solution followed by contact with an aqueous ammonium ion solution.
In accordance with U.S. Pat. No. 4,503,023, aluminum from AlO.sub.4 -tetrahedra of zeolites is extracted and substituted with silicon to form zeolite compositions having higher SiO.sub.2 /Al.sub.2 O.sub.3 molar ratios. The preparative procedure involves contact of the starting zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of about 3 or greater with an aqueous solution of a fluorosilicate salt using controlled proportions and temperature and pH conditions which are intended to avoid aluminum extraction without silicon substitution. The fluorosilicate salt serves as the aluminum extractant and as the source of extraneous silicon which is inserted into the zeolite structure in place of the extracted aluminum.
U.S. Pat. No. 4,427,790 describes a process for improving the activity of crystalline zeolites in which the zeolite in the "as synthesized" form or following ion-exchange is reacted with a compound having a complex fluoranion.
The use of chelating agents to remove framework and non-framework aluminum from faujasite materials is shown by G. T. Kerr, "Chemistry of Crystalline Aluminosilicates. v. Preparation of Aluminum Deficient Faujasites", 72 J. Phys. Chem., 2594 (1968); T. Gross et al., "Surface Composition of Dealuminized Y Zeolites Studied by X-Ray Photoelectron Spectroscopy", 4 Zeolites, 25 (1984); and J. Dwyer et al, "The Surface Composition of Dealuminized Zeolites", 42 J. Chem. Soc., Chem. Comm. (1981)
Other references teaching removal of aluminum from zeolites include U.S. Pat. No. 3,442,795 and U.K. Patent No. 1,058,188 (hydrolysis and removal of aluminum by chelation); U.K. Patent No. 1,061,847 (acid extraction of aluminum); U.S. Pat. No. 3,493,519 (aluminum removal by steaming chelation); U.S. Pat. No. 3,591,488 (aluminum removal by steaming); U.S. Pat. No. 4,273,753 (dealuminization by silicon halides and oxyhalides); U.S. Pat. No. 3,691,099 (aluminum extraction with acid); U.S. Pat. No. 4,093,560 (dealuminization by treatment with salts); U.S. Pat. No. 3,937,791 (aluminum removal with Cr (III) solutions); U.S. Pat. No. 3,506,400 (steaming followed by chelation); U.S. Pat. No. 3,640,681 (extraction of aluminum with acetylacetonate followed by dehydroxylation); U.S. Pat. No. 3,836,561 (removal of aluminum with acid); German Patent No. 2,510,740 (treatment of zeolite with chlorine or chlorine-containing gases at high temperatures); Netherlands Patent No. 7,604,264 (acid extraction); Japan Patent No. 53/101,003 (treatment with EDTA or other materials to remove aluminum); and 54 J. Catalysis, 295 (1978) (hydrothermal treatment followed by acid extraction).
The use of ZSM-5 zeolites in the conversion of olefins to provide lubricating oils is known, inter alia, from U.S. Pat. Nos. 4,520,221 and 4,524,232. In the former, surface acidity of a ZSM-5 zeolite catalyst is neutralized by treating with a sterically hindered base such as 2,6-di-tert-butylpyridine. Employing the base-modified catalyst, propylene was converted to lubes with a 60 VI number increase over a lube oil prepared with the unmodified catalyst. The base must be added continuously during the conversion process. At high reaction severities, the base will react with the feed, a practical limitation on the use of such a catalyst.